Shock absorber



July s, 1945.

E. F. RossMAN 2,379,750

sHoox A'BsoRBER Filed Sept. 22, 1943 2 Sheets-Sheet 2 l HTTORNEYS.

Patented July 3, 1945 SHOCK ABSORBER Edwin F. Rossman, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application September 22, 1943, Serial No. 503,379

14 Claims. (Cl. 188--88) This invention relates to improvements in hydraulic shock absorbers and particularly to the two-way direct-acting type of shock absorbers.

It is among the objects of the present invention to provide a hydraulic shock absorber adapted to control both the approaching and separating movements of two relatively movable members such as the frame and axle of a vehicle. The shock absorber is particularly adapted to provide a slight resistance to movements in either 1o through the piston taken along the line and in direction from its dead center or normal load the direction llll of Fig. 7.

position, and comparatively higher resistance Referring to the drawings, the working cylwhile moving through a predetermined nal porinder of the shock absorber is designated by the tion of its range of movement in either direction. numeral 20. This cylinder is provided with a A further object of the invention is to provide 15 head or end member at each end, the upper end a hydraulic shock absorber having compression member being designated by the numeral 2|. One or approaching and rebound or separating end of this end member 2| is machined to promovements, said shock absorber during its comvide an annular projection 22 which lits snugly pression stroke from normal load position prointo the one end of the cylinder and. is attached viding a low resistance to movements for a preto said cylinder by Welding or any other suitable determinedA portion of such stroke and then a method. The outer diameter of the-annular body comparatively high resistance for the remaining portion of end member 2| is of comparatively and rial portion of its compression stroke. When greater diameter than the Working cylinder 20 moving from normal load position through its and is provided With threads fOr receiving the rebound stroke, the shock absorber provides a nteriorly threaded end of the tubular member comparatively low resistance to movement 24. Tubular member 24 as shown in Fig. '1 surthrough a predetermined portionI of this stroke rounds the cylinder 20 and, due to the diilerence and then through the final remaining portion of l in diameter of said cylinder and tubular memthe rebound stroke it provides an increased reber, an annular space 25 is provided :forming the sistance. This increased resistance may not fluid reservoir'.` The outer surface of the end necessarily be as high as the resistance oiered l member 2| is recessed as at,26, this recess comduring the nal stage of the compression stroke. municating and aligning with a central bore 21 Further objects and advantages of the presthrough the head member. Recess 26 and bore ent invention will be apparent from the follow- 21 are concentric and coaxially align with the ing description, reference being had vto the ac- 35. working cylinder 20. A packing gland 28 is Vrecompanying drawings wherein a preferred emceived by the recess 26. Ducts 29 iin the said bodiment of the present invention is dearly member 2| provide communication between the shown. bottom portion of the recess 26 and the reser- In the drawings: voir 25. Any suitable type of packing 30 is pro- Fig. l is a sectional view taken longitudinally 4o vided in the reservoir 25 adjacent the annularthrough the shock absorber. To illustrate the point of engagementbetween the end member 2| shock absorber completely this view is at halfand tubular member 24 to prevent uid leaks size scale. All the remaining views of the drawthrough the screw threaded connection between ings are made at full size scale. said two members.

Fig. 2 is a fragmentary, sectional view par- 45 vA piston rod 'l0 slidably extends through the ticularly illustrating the valve head or end mem' packing gland 28 and the central bore 21 in the ber of the working cylinder, end member 2| into the interior of the cylinder l Fig. 3 is a transverse and sectional view taken 20. The outer end of this piston rod 'l0 has an on the line 3-3 of Fig. 1. attachment xture 3| secured thereto in any Fig. 4 is a detail sectional view of the `shut-off 50 suitable manner, this attachment fixture provalve carried by the piston rod. viding means for securing the movable member or Fig. 5 is a Vsectionalrview of the piston taken Apiston of the shock absorber to one of the'relaalong the lines 5-5 of Fig. 6. y tively movable members, as for instance the frame Fig.v 6 is a view of the lower or compression of a vehicle. This attachment fixture has an anside of the piston.

Fig. 9 is a detail sectional view particularly illustrating the piston assembly. The cross section of the piston was taken along the line 9--9 of Fig. 6.

Fig. 10 is a view similar'to Fig. 9, the section nular .disc-like 'langeV 32 vwhich lits into a tubular member'33 of greater diameter than the tubular member 24 surrounding the working cylinder 28. Tube 33 may be attached to the attachment fixture 3| by welding as at 34. This tubular member 33 telescopically fits over the tu- 'bular member 24 a predetermined length, there-y cylinder 28. A portion of the lower surface of said end member 35 is seated upon the inner surface of the lower attachment fixture 31 by. means of which this end of Vthe .shock vabsorber is attached to the other relatively movablemember to'be controlled,` as for instance .the axle of the vehicle.

The outer diameter of this fixture 31 is such as to fit snugly into. the `tubularmember 24 which is attached to the xture 'by welding as at 38. A central recess- 39 in the fixture 31 is in communication with the reservoir 25 receiving the one endconvolution of lajfspring'fz. A portion of the end member isspun overas* at .63; `forming a retaining 4lip which securely attaches member 35. As shown 'in Fig. 1 the upper `corr-I.

through radial slots 48 cut in 'the inner end vsurwith valve seats and fluid passages as follows: a i

plurality of fluid passages 42 entendv through the end member 35, these fluid passages being' arranged ln an annular row as shown in Fig. 3.

Another group of fluid passages 43 of greater fluid flow capacity than the fluid passages '-42 are ar' ranged in an annular row outside the .annular row of fluid passages 42. An annular ridge 44 is provided in the bottom wall surface -of the recess 4|, this annular ridgelying just outside the confines of the fluid flow passages -43 so as of lesser diameter than the annular ridge-44,'lies just inside the confines of the annular row of fluid passages 43. Thus the concentric annular ridges 44 and 45 provide an annular space .therebetween into which the one end of all the fluid passages 43 open. These two concentric annular ridges 44 and 45 being of substantially inverted V-shape cross section as shown in Fig. 2, provide valve seats for the ring-shaped intake valve 46 which is normally urged upon said annular concentric valve seats 44 and 45 by a spring 41 interposed between the valve 46 and a ringshaped retainer washer 48 secured to the end member by a spun-over edge 49. The outer diameter of the intake valve 46 is substantially less than the diameter of the recess 4|, but'still sufficient to engage the outer annular valvel seat 44. Spaced humps in the outer periphery of the intake valve 46 maintain the valve in proper alignment so as to assure engagement of the valve 46 with the annular valve seats 44 and 45 and still maintain a proper fluid flow gap between the inner wall of the recess 4| and the outer edge of the valve 46.

The lower or outer ends of fluid ow passages 42 terminate in a flat surface of an annular extension 58 on the end member. A similar annular extension-5| is provided on the opposite, inside surface of the end member 35, the surface of extension 5| being substantially flush with the faces of the annular valve seats 44 and 45. The

inner ends of fluid passages 42 terminate at this inner surface of the annular extension 5|.

Reference to Fig. v3 shows that the surface of the annular extension 5| has two counterbores 52 and 53,leach of these counterbores lbeing substantially concentric with a fluid passage 42. This of any air in said fluid from the reservoir' through to encompass them. Another annular ridge 45, i

of the valve 61 being spun over to` securefthe upper-'end convolutionof spring 62A to sai'divalve. This spring 5 2 vis of lesser diameterathanthe .inner'diameter of Athe cylinder 28 and is' ofsuch length so as yieldably to suspend thevalveu -a predetermined distance -fromthe end-member in the reservoir 25a predetermined distance zffroin the-bottom end member 35, this washer 69" acting:

tween the tubular member 24 and saidwasher lpermit any -fluid leaking past the piston .rod` bearing 21 to return to the reservoir fluid supply.,l

provides for a fluid flow orifice, as will later be described. Y A central bore in the end member 35 is interiorly threaded to receive the threaded shank 5 5 of a stud having a main cylindrical shaped body portion 56 and a larger head 51. A sleeve valve 58 is slidably mounted upon the vbody portion 56` i of the stud, this sleeve valve 58 having an out-' wardly extending, annular flange 59 .wh`ich is` u urged into seating engagement with the surface I -of the annular extension 58 on the end member-1 35 by a spring 68 so that normally the outerlends of the fluid flow passages 42 are yieldably/held; yclosed by the flange 59 of this valve.

Anannular groove 6| .is providedinjthe'iinner surface of the end member 35,.this`annular grooye the end convolution of the spring. 82 to the .en d

volution of spring 62 is secured in a groove .5 6 provided in theA ring-shaped valve 61, .portions g 35. The function of' valve'. 61 ,will be` ibeddetailedly hereinafter..`

A cylindrical cup-shaped washer 69 isfsupportd as a dash for preventing extreme fluidjagltation in, they reservoir 25 and still permit the v.escape the ducts 29. Clearances in the washer- 69y bevia'the ducts 29 in the-head member 2|.

The piston rod 18 extends into the interiorlot e.

the cylinder 2|),y the inner end of said pistonjrodf. i-'f 'i Y" having a reduced diameter portion 88 A providing an annular shoulder 8| spaced a predeterminedl distance from the end of the piston rod. "--A spacing collar 82 flts snugly over the reduced;

diameter portion 88 of the rod 18 and abuts the shoulder 8| on said rod. This spacing collar 82 has a reduceddiameter portion 83 upon-,which is slidably mounted a valve 84 having anr out-.

wardly extending annular flange 85 ,which is urged upon the upper surface of the piston 38 by. v

a spring 8 6 interposed between the head portion ofthe spacing collar 82 and the flange85 of the valve 484. Valve 84 normally yieldably closes certain fluid flowgpassages to the piston, as w'illbe i described. i

The piston 98 has a central bore 9| which snugly fits about the reduced diameter portion 88 ofthe piston rod. The piston is maintained in engagement with the inner end of the spacing collar 8 2 by another spacing collar 81 interiorly threaded to be screwed upon the threaded end of the rewith particular. reference to the gures on the second sheet ofv drawings, said iigures' including those numbered 5y to 10 inclusive, it will be seen that the piston is provided with a plurality of radial recesses extending from the outer annular surface of the piston short of the central bore 9|. These radial recesses are substantially intermediate the end walls of the piston and, for purposes of description, are designated by the nu-r merals |00, |02, |03, |04, |05, |06, |01, |08, |09, ||0 and Certain other fluid flow passages lead from the opposite sides of the piston in communication with these radial recesses. The Figs. and 6 illustrate particularly the iiuid ow passages providing communication from the lower .or compression surface of the piston with said radial recesses. The rst group of such fluid ow passages are arranged in a circular row immediately about the piston rod. 'I'hese passages are as follows: |2| communicates with 'radial recess 0|; |23 communicates with recess |03; |25 with recess' |05; |21 with recess |01; |29 with recess |09 and |3| with recess Two other fluid flow passages of greater transverse di-mension and therefore greater iluid ilow capacity than the group just referred to lead from the compression side surface of the piston 90 into certain radial ducts, these two fluid ow passages being diametrically opposite each other and at somewhat greater distance from the center of the piston rod than the annular row of fluid flow passages previously described and numbered |2| to |3| inclusive. One of these larger uid ow passages is designated by the numeral |22 and communicates with recess |02. metrically opposite fluid ilow passage |28 communicates with the recess |08. Four more uid flow passages of substantially the same iiuid ow capacity as passages |22 and |28 provide communication between the lower compression surface of the piston 90 and certain radial recesses. -These four fluid flow passages are arranged in an annular row and are spaced stilla greater distance from the center of the piston rod than the vfluid ilow passages |22 and |28.v One of these most outwardly positioned iluid passages is designated by the numeral and communicates with radial recess |00, the second, |24, communicates with radial recess |04,the third passage |26 is diametrically opposite the passage I 20 and it communicates with the radial recess |06. The fourth passage diametrically opposite passage |24 communicates with radial recess ||0.

The spring loaded pressure relief valve 89 normally yieldably closes the fluid passages |2| to |3| inclusive, Fig. 10 showing the passages |23 and |29 of this group being closed by valve 89. When the piston reaches a predetermined point in its downward movement within the cylinder 20, it will engage the ring valve 61 yieldably supportedwithin the cylinder by the spring 62, said ring valve then closing the fluid passages |20, |24,

The other dia- |26 and |30'in 'the piston and partially covering the fluid passages 22 and |28. This is clearly illustrated in the Fig. 9.

Figs. 7 and 8 illustrate the piston and particularly its upperor rebound side and uid passages. Here an annular row of fluid passages similar to the passages |2| to |3| inclusive are provided, i

these passages communicating with radial recesses alternate to the recess with which passages |2| to |3| communicate. Referring to Fig. '1, the

passage 200 communicates with recess'l00; the passages 202 with recess |02; passage 204 with recess |04; passage 206 with recess |06; passage 208r with recess |08 and passage 2|0 with recess |0. Three fluid now passages similar to uid ilow passages |22 and |28 are provided on this side of the piston` at a distance equal from the center as said passages |22 and |28, one of these passages being designated by the numeral 203 communicating with passage |03, the other 201 communicating with recess |01, and passage 2|| communi eating with recess Three more passages similar to passages |20, |24, |26 and |30 on the opposite side of the piston are provided on this rebound side, the one designated by the numeral 20| communicating with recess |0|; 205 communicating with recess' |05, and 209 communicating with recess |09. The spring loaded uid relief valve 04 normally yieldably maintains passages 200, 202, 204, 206, 209 and 2|0 closed as shown in Fig. 9. The upper end member 2| and particularly the portion thereof extending into the cylinder -20 has a collar v| 50 secured thereto in any suitable manner, this collar forming an anchorage for the upper end of a coil spring |5|. the lower convolution or end of said spring being secured to the ring valve |52. This spring holds ring valve |52 yieldably a predetermined distance from the upper end member 2|, When the piston moves upwardly it may engage this ring valve |52, and when it does, said valve will close the uid passages 20|, 205 and 209 completely and will partially close the fluid passages 203, 201 and 2|| so as to reduce their iluid ilow capacity.

The inner end of the piston rod 10 is centrally recessed as at |60. A collar |6| is threaded into the spacingcollar 01 so as to abut the end of the piston rod 10. This collar |6| has a central bore of two different diameter portions, the portion adjacent the outer end of the collar being smaller in diameter than the inner portion of tl'ne bore, thus presenting an interior shoulder |62 within the collar. A spindle |63 extends loosely into and through the collar |6|, the'inner end of this spindle having an enlarged head portion |64 of slightly less diameter than the recess |60 in the piston rod so that the shoulder provided between the smaller body portion of the spindle |63 and" tbe larger head .portion |64 of said spindle engages the shoulder |62 which acts as a stop preventing removal of the spindle from the collar |6| when once assembled. This spindle |63 has av shut-off valve |66 loosely mounted thereon, the spun-over end of the spindle preventing removal of the valve therefrom. A coil spring |61 is interposed between theshut-oi valve |66 and the collar 6| and yieldably maintains said collar in engagement with the spun-over end of the spindle. Valve |66 is movable to engage the end member and particularly the portion 5| thereof in which fiuid passages 42 terminate when the piston reaches a predetermined point in its downward, compression movement, as will detailedly be described.

As has been stated previously, the function of this shock absorber is to control the` movements The fixture nism so that the shock absorber will offer resistance inaccordance with the fluid flow thereby controlling the relative movements of theg frame and axle of the vehicle. Y

Considering for purposes of description that the shock absorber `as shown in Fig. l is in the normal load position and considering that the wheels of the vehicle strike an' obstacle in the roadway, thrusting the axle upwardly, a movement of the cylinder assembly upwardly relatively to the piston will obtain. This is equivalent to a downward movement of the piston in the cylinder.` As the piston moves downwardly in the cylinder 20 it willl exert pressure upon the fluid therebeneath. Under these circum- 1 stances under the effect of spring 41 and with the aid of fiuid pressure, valve 4 6 is urged upon its annular valve seats 444 and 45 thereby to prevent any fluid flow from the cylinder 20 I through the valve passages 43 into the reservoir.

The spring load on the pressure relief valve 58 is greater thanthe spring load upon the pressure relief valve 84 in the piston, thus said valve 84 will be actuated to become effectiveto establish a fluid flow through the piston before the valve 58 becomes effective to establish a fluid flow from the cylinder through passages 42 in the end mem.. ber 35 into the reservoir. In response to the downward movement of the piston 90 and at a predetermined fluid pressure-within the lower workingV chamber of the cylinder, valve 64 will be moved from its seat, the fluid pressure beneath the cylinder acting through the uid passages respective radial recesses |00, |02, |04, |06, |08 and I! connect said uid passages with the exhaust fluid passages 200, 202, 204, 206, 208 and 2|0 normally closed by the spring loaded valve 84. When the pressure reaches a predetermined value, this valve 84 will be lifted from engagement with the piston and thereby open the exhaust passages 200, 202, 204, 206, 208 and 2|0 to permit a restricted fluid 110W therefrom into the upper working chamber of the cylinder. However, the cylinder chamber above the piston cannot receive all of the fluid displacedv from the cylinder chamber beneath the piston, for the upper working chamber is of lesser fluid capacity than the lower working chamber due tothe presence of the piston rod 10 which displaces fluid I in this upper chamber. The fluid displaced by the piston rod 10 in the upper' chamber will therefore cause excessive fluid under pressurel in .the

lower cylinder chamber to move valve 58 from its seat on surface 5| of the end member 35 against the effect of spring 60, thereby establish,

ing a pressure relieving flow from the cylinder through the fluid flow passages 42 past the valve 58 and through channels 40 into the reservoir 25. The restriction to the fluid flow from the lower cylinder chamber into the upper cylinder chamber'by valvev 8 4 and the restriction to the fluid flow from the lower cylinder chamber into the reservoir past valve 58 are of such a degree .stages of resistances are provided.

closed, the other two by virtue of the counterbores 52 and 63 permitting a restricted fluid flow against and past the valve 58 into the working cylinder. Thus after valve |66 is seated, the effective area of valve 58 is greatly reduced and therefore the fluid flow in the shock absorber is more highly restricted consequently the shock absorber will now offer a greater resistance to relatively approaching movements of the frame and axle ofthe vehicle. Continued movement of the piston downwardly will cause the spring |61 to maintain the valve |66 upon the seat 5| while the stem |63 slides upwardly into the recess |60 of the piston rod. When, in the downward movement of piston 90, it reaches a predetermined point, ring valve 61 will be engaged, this ring valve closing certain of the entrance uid ow passages at the bottom or compression side of the piston while restricting others. The passages that are completely closed are numbered |20, |24, |26 and |30 while the passages which are partially restricted are the passages |22, and |28. By restricting passages |22 and |28 and completely closing the other passages |20, |24, |26 and |30 the effective volume of' fluid acting upon the pressure relief valve 84, which controls the outlet end of all these passages at the upper compression side of the piston, will be greatly reduced,A thus at the existing pressure the spring 86 willactuate the valve 8,4 increasingly to restrict the fluid flow and consequently the shock absorber will provide an increased resistance to further approaching movements of the vehicle frame and axle. 'This increased resistance will be maintained while the piston moves from the point of contact with the ring valve 61 throughout-its final range to the extreme end of the compression stroke, or more specifically until the piston 90 reaches al predetermined limit in its downward stroke. Thus it may be seen that during the downward stroke of the pistonthree The first, from normal load position to a position in which valve |66 engages end member 35 which is a stage of minimum resistance, the second or intermediate stage where valve |66 actually engages seat 5| provides an increased resistance over that flrst offered by the shock absorber, and the third or final stage of resistance, which is the highest resistance and which is provided by the shock abcapacity completely to flll the lower chamber due.

to the presence of the piston rod 10 in the'upper chamber and therefore the intake valve 46 will be lifted from its annular seats 44. and 45 against the effect of spring 41 to establish a flow of fluid from the reservoir 25 through channels 40 and fluid flow passages 43 into the cylinder chamber beneath .the piston. As the pressure is exerted upon the fluid in the upper chamber of the working cylinder 20, fluidwill be urged through the passages 20|, 203, 205, 201, 209 and 2| into the communicating radial recesses |0|, |03, |05, |01, |09 and From these radial recesses fluid will flow through the exit ports or passages |2|,

|23, |25, |21, |29 and |3| terminating in the bottom side of the piston andnormally yieldably closed by the spring loaded pressure release valve B9. At a predetermined fluid pressure this pressure relief valve 89 will be moved against the effect of its spring 92 to permit a restricted now of fluid from the exhaust ports mentioned,

thereby establishing a controlled fluid flow from the upper cylinder chamber through the piston into the lower cylinder chamber. This causes the shock absorber to offer its first stage of rebound movement resistance, which resistance is comparatively light in accordancegwith the design of the spring loaded valve 89. Continuing to move upwardly, the piston 9U will, when it reaches a predetermined point, engage the ring valve |52 suspended at a predetermined distance from the top of the cylinder chamber by the spring When ring valve |52 engages the piston the following fluid entrance passages 205A and 209 will be completely closed, as is illustrated in Fig. 10. 'I'he entrance passages 203, 201 and 2| will be partially covered by the ring valve |52. The closing of some and partial covering of others of the entrance passages will substantially reduce the effective area of the spring loaded pressure relief valve 89 and consequently it will become effective at this point to increase its restriction to fluid flow from the upper cylinder chamber through the piston into the lower cylinder chamber. Thus as the piston moves from the point of contact with ring valve |52 to the extreme upper limit of the rebound stroke, uid ow to the piston will be restricted to a lgreater degree than before and consequently the shock absorber during this stage of movement will 4offer an increased resistance to the separating movement of the frame and axle of the vehicle. From this it may be seen that the shock absorber on its 'rebound movement offers a predetermined low resistance to the separating or rebounding movement of the relatively movable members for a predetermined portion of this movement, and then for the final portion of this rebound movement the resistance offered by the shock absorber is substantially increased.

The aforegoing description clearly discloses applicants shock absorber as being adapted to provide a 3-stage compression movement control and a 2-stage rebound movement control, the resistance offered by the shock absorber approaching the final stages of both movements being the highest, that is greater than resistances offered during the other intermediate or initial portions of its movement in the same direction.

While the embodiment of the present invention as herein disclosed, constitutes la preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows: l

l. A hydraulic-shock abosrber comprising in combination, acylinder having an oriflced end member communicating with a fluid reservoir, fluid displacement means in said cylinder comprising a piston having a plurality of fluid transfer passages and a rod for reciprocating said piston; a fluid flow controlling device yieldably urged upon each side of the piston, each device normally `yieldably closing one end of a group of said passages; means yieldably supported in the cylinder adjacent each end, said means beingadapted to engage the side of the piston adjaon said side of" the pistonfor reducing the effective volume ol' uid acting upon the fluid flow controlling device yieldably urged upon the opposite side of the piston; and means for controlling fluid flow through the orificed end member into and from the reservoir.

2. A hydrauiic shock absorber comprising in combination a cylinder having an oriflced end member communicating with a fluid reservoir; a piston in said cylinder, said piston having a plurality of passages therethrough; an actuator for reciprocating said piston; means yieldably urged upon the opposite sides of the piston, each means normally closing one end of a group of said passages; and means for restricting the opposite f open ends of each group of said passages when the piston reaches a predetermined point in its movement toward either end of the cylinder, said means being yieldably supported in the cylinder adjacent each en d thereof; and means for controlling lfluid flow through the oriflced end member in, either direction.

3. A hydraulic shock absorber comprising in combination, a cylinder, a piston in said cylinder, said piston having a plurality Vof through passages, a piston actuator; spring loaded means normally closing a different group of said passages at each side of the piston; spring suspended means in the cylinder adjacent each end thereof, each adapted to restrict the open end df the group of passages normally closed at the opposite end by the spring loaded means on the side of the piston opposite the suspended means whereby the effective volume of fluid acting upon said spring loaded means is reduced during a predetermined nal range of piston movement toward said suspended means; and a valved end member for said cylinder, for controlling fluid flow into and fromv said cylinder.

4. A hydraulic shock absorber comprising in combination, a cylinder, a piston in said cylinder, said piston having a plurality of fluid transfer passages; a' piston reciprocator; a spring loaded, pressure relief valve on each side of the piston, each valve normally closing certain of said piston passages but adapted to permit a restricted fluid iiow through said certain piston passages in one direction in response to piston movement in the opposite direction respectively; a ring valve yieldably suspended in each end of the cylinder, and adapted to be engaged by the piston and predeterminately restrict uid flow against the pressure relief valve on the side of the piston opposite the ring valve while the piston moves through a predetermined I'lnal portion of its range of movement; a uid reservoir; and a valved end member provided between the cylinder and reservoir for controlling fluid flow between the cylinder and reservoir.

5. A hydraulic shock absorber comprising in combination, a cylinder; a closure membe-r for each end of the cylinder; a piston in said cylinder, said piston having a plurality of passages for the transfer of fluid from one side of the piston to the other; a piston rod slidably extending through the one closure member; a pressure relief valve on each side of the piston, one controlling fluid ilow in gne direction through certain of said piston passages, the other controlling the flow in the opposite direction through the other of said passages, said fluid flow being established in response to reciprocation of the' piston in the cylinder; a ring plate in the cylinder on each side of the piston; a spring secured to each closure member and to the ring' plate adjacent thereto for supporting the ,ring plate, each of which is adapted tO engage the piston when it is moved into proper position in the' cylinder for closing certain of the fluid passages in the piston whereby the effective volume of lluiddirected against the pressure relief valve on the side of the piston Aopposite the lactive ring plate is predeterminately reduced;

and valved ducts in the other closure member for controlling fluid flow into and from the adJacent cylinder chamber.

6. A hydraulic shock absorber comprisingin combination, a fluid reservoir; a cylinder having an oriflced end member providing communication betweenthe reservoir and cylinder; fluid displacement means in -said cylinder comprising a piston and a piston rod, said piston having a p lurality of fluid passages therethrough; a spring loaded pressure relief valve on each side of the piston each valve normally closing the ends of half of the piston passages; a spring suspended valve adjacent each en of the cylinder adapted to be engaged by the pis when moved 1n one direction or the other for closing some of the pistn passages normally closed by the pressure relief valve on the opposite side of the piston; a valve on the end member for permitting fluid flow substantially freely .from the reservoir through certain orifices in said end member mto Y the cylinder as the piston moves away from said end member; and a spring loaded 4pressure relief valvenormally closing the other orifices 1n said end member and adapted to permit a restricted fluid flow from said cylinder into the reservoiras the piston is moved toward said end member.

7. A hydraulic shock absorber comprising in combination, a fluid reservoir; a cylinder having an end member providing fluid passages connecting the reservoir and cylinder; a piston in said cylinder having a plurality of fluid passages therethrough; a rod for reciprocating said piston; pressure relief valves for controlling the flow of fluid .through the piston .passages as the piston is reciprocated; control valves suspended in the cylinder. for restricting certain of the piston'passages as the piston is moved through a final portion of its range of movement in either direction; a valve on said end member for permitting a substantially unrestricted fluid flow from the reservoir into the cylinder as the piston moves away from said end member; and another valve on said end member for lpermitting a restricted fluid flow from the cylinder into the reservoir as the piston moves toward saidend member.

8. A hydraulic shock absorber comprising'm combination, a. fluid reservoir; a cylinder having an end member providing fluid passages connecting the 'reservoir and cylinder; a piston in said cylinder having a plurality of fluid passages therethrough; a rod for .reciprocating sa1d plston; pressure relief valves Afor controlling the. flow of fluid through the piston passages as the piston is reciprocated; control valves suspended 1n the cylinder for restricting certain of the p1ston passages as the piston is moved through a final portion of its range of movement in either direction;

a check valve yieldably urged upon said end 9. A shock absorber in accordance with claim 8, in which, however, there is provided a valve, carried by the piston rod and adapted to render the pressure relief valve on the end member substantially ineffective when the piston is moved lto apredetermined point relative to said end member and while the piston is moving the remaining-portion of its range of movement toward saidend member.

10. Ashock absorber in accordance with claim 8, differing, however, in that a valve is yieldably carried by the piston rod for engaging the end member at a predetermined point in the movement of the pistonwtoward said end member whereby substantially to close the fluid passages normally closed bythe pressure relief valve on said member and therebyl rendering said pressure relief valve substantially ineffective during the final portion of the piston movement toward said end member.

11. A shock absorber in accordance with claim 8, differing, however, in that a spring loaded valve is yieldably supported by the piston rod, said valve being adapted to engage the end member when the piston has been moved into a predetermined position relatively thereto, for reducing the eective area of the fluid passages in the end member, normally-closed by the pressure relief valve on said member, during the remaining portion of the range of piston movement toward said end member.

12. A hydraulic shock absorber comprising in combination, a fluid reservoir; a cylinder having an end member provided with a plurality of fluid passages connecting the reservoir with the cylinder; fluid displacement means in said cylinder comprising a piston and a rod for reciprocating urged upon each side of the piston each means normally closing one half of the piston passages member normally to close certain of its fluid respectively; ring valves yieldably suspended in.

the cylinder at predetermined positions on each side of the piston and adapted to engage the piston and restrict certain fluid passages therein while the piston moves through a final portion of its range of movement in either direction whereby a lesser volume of fluid is directed against the respective fluid flow control means to establish restricted fluid flows therethrough; a valve on the cylinder side of the end member, yieldably closing certain of the uid passages therein; a valve on the reservoir side of the end member yieldably closing the other of the fluid passages therein; and a valve supported by the piston rod for closing certain of said other uid passages in the end member while the piston is moved through a predetermined final portion gf its range of movement trvard said end mem- 13. A hydraulic shock absorber comprising in combination, a uid reservoir; a cylinder. havingan end member providing fluid passages connecting the reservoir and cylinder; a piston in said cylinder having a plurality `of fluid passages therethrough; a rod for reciprocating said piston;

pressure relief valves for controlling the flow of j fluid through the piston passages as the piston cally supported in the piston rod; a valve at the outer end of said stem; and a spring interposed between the valve and piston rod, said spring urging the valve upon the end member to close some of the lluid passages, normally closed by one ol' the spring loaded valves on the end member, only while the piston is actuated through a predetermined llnal portion of its range of movement toward said end member.

14. A` hydraulic shock absorber comprising in 10 to the piston for actuating it; a spring loaded valve norma11y.'yieldab1y urged against each side of the piston, each valve closing the one end of alternate piston passages; and means independent of but engageable by the piston as it reaches a predetermined point in its travel in elther direction, for restricting the normally open ends oi' certain of said alternate uid ow passages whose oppositeends are normally closed by the spring loaded valve engaging the side of the piston opposite said means. y 

